The present invention relates to a directional coupler with an interaction space having two ends or sides, at each of which two hollow guides are coupled and in which the interaction space has dimensioned such that the higher wave types TE11 and TM11 modes can be propagated as well as the fundamental wave type TE10 mode.
This type of directional coupler is known from and described in German Published Patent Document 11 26 461. This directional coupler comprises two rectangular hollow guides, which are arranged with wide sides there of adjacent to each other. An opening is provided in the common separating wall of the hollow guides, which forms an interaction space, in which higher wavw mode types, such as TE11 and TM11 modes, can exist as well as the fundamental mode TE10. According to the state of the art the separating wall between the hollow guides must be as thin as possible in order to keep the irregularities at the transition points between the hollow guides and the interaction space very small for extensive reduction of reflections. The directional coupler described in this reference is disadvantageously very narrow band.